MEMS structural components of the type discussed here may—depending on the configuration of the component structure—assume both actuator functions and sensor functions. Thus, such a MEMS structural component may be configured, for example, as a valve component, in which the diaphragm is used as a closure element. In this case, the capacitor system is used for selectively activating or actuating the closure element. In another actuator application, the diaphragm of the component structure functions as a speaker diaphragm and is activated with the aid of the capacitor system. A MEMS structural component of the type discussed here may, however, also be configured as a pressure sensor or a microphone structural component. In these applications, the diaphragm is used for signal detection in that the deflections of the diaphragm caused by pressure or sound pressure are detected as capacitance changes of the capacitor system.
In WO2010/139498A1, a MEMS structural component of the above-named type is described, a microphone structure including an acoustically active diaphragm and an acoustically permeable counter-element being implemented in the layered structure of the MEMS structural component. In this case, the diaphragm is formed in a diaphragm layer above the base substrate of the structural component and spans a sound opening in the rear side of the substrate. The counter-element is implemented in another layer above the diaphragm. The diaphragm functions as a movable electrode and, together with a fixed electrode on the counter-element, forms a capacitor system for signal detection.
Since the counter-element of the known MEMS structural component is formed in another normally relatively thick layer of the layered structure, it contributes significantly to the overall height of the structural component. The manufacturing of the known MEMS structural component also proves to be problematic in several respects. The counter-element is, in this case, only applied after the diaphragm in the layered structure of the structural component. For that purpose, a relatively thick layer, as for example in an epi-polysilicon layer, is normally applied to the layered structure, since the position fixing of the counter electrode is a requirement for reliable signal detection. The deposition of such an epi-polysilicon layer requires very high process temperatures which have an adverse impact on the properties of the already produced diaphragm. Furthermore, these high temperature steps are relatively complex in terms of manufacturing, as is also the structuring of the relatively thick counter-element layer and the production of the rear side sound opening in a rear side etching process.